At the present time it is the common, if not universal, practice to provide the lower ends of concrete piers which constitute the foundation for a building with conical formations which resemble a bell and are commonly so called by those working in this art. A pier with a bell thereon is formed at the same time by pouring concrete into a cylindrical pier bore having a bell shaped recess at its lower end.
Ordinarily the cylindrical pier bore is first formed by an auger and extends from the ground surface to the rock bed or other earth formation which is to support the pier. The bell shaped recess is formed usually by rotating one or more blades that are pivotally mounted at their upper ends and gradually swung outwardly by eccentric links. These cutting operations create spoil which must be removed.
One school of removing the spoil is to use a liquid such as water or drilling mud and operations of this type are confined to offshore drilling for oil wells. They clearly are not susceptible for use for the formation of piers as a support for buildings in locations removed from the coast and structures not related to oil wells.
Another method of operation is to remove the bell cutting apparatus after a portion of the bell shaped recess is formed and then removing the spoil so far formed. The removal of the spoil often requires the entry of a man into the lower end of the bore. Even should manual operations not be required for the spoil removal, safety regulations now obtaining in most jurisdictions require that the bell recess be inspected at several stages of its formation. Thus in some jobs it has been necessary to withdraw the belling apparatus and remove the spoil as many as fifty times in the formation of a single bell recess. These repeated entries of a man into the excavation constitute an impairment of the safety factor to a high degree.
Another undesirable phase attending the cutting of bell shaped recesses in accordance with present use of cutting blades of the type noted, is the danger of over-cutting. Bells are designed for a certain angle of the conical end portion. Should the cutting blades be swung out to an angle in excess of that of a particular bell, the recess will not have the required shape and great difficulty is experienced in correcting such an error.
The known art is notably lacking in apparatus which is effective to cut a bell shaped recess at the lower end of a pier bore on what might be called a single downward pass of the apparatus and at the same time remove the spoil.